US3374128A - Stabilized blasting compositions containing at least one iron sulfide and an antacid - Google Patents

Description

3,374,128 Patented Mar. 19, 1968 United States Patent ()titice ABSTRAfJT OF THE DISCLOSURE This invention relates to stabilized blasting composit1ons of high bulk density and high explosive strength containing iron sulfide and antacid stabilizer therefor.

A primary function of an explosive charge in blasting operations is to provide the energy required to release material from its natural formation and to render the material in a form in which it can be handled and processed with minimum difiiculty. The cost of recovering the desired material in usable form depends, to a large extent, -on the cost of the blasting composition used and the cost of preparing the site ofthe blasting operation. For this reason, much effort has been expended to develop blasting compositions using relatively inexpensive ingredients which produce high energy and are of high density. Such compositions permit increased borehole spacings without increasing hole diameter and thereby decrease the cost of preparing the blasting site. In addition to being of low cost, however, the blasting composition must also be capable of being formulated, stored, and handled with a minimum safety hazard. The use of dense metal sulfides as metallic fuels has been proposed in blasting compositions also comprising an inorganic oxidizing salt and one or more other fuels. However, in spite of the low cost and relatively high density of metal sulfides such as iron pyrites, their use in blasting agents has been curtailed since they candecompose or react spontaneously with other ingredients of the composition with the evolution of heat. Particularly in hot mixing of the ingredients or heated storage of the product, sufiicient heat can build up to cause fume-offs, fires, and, under severe conditions, premature detonation of the composition. Accordingly, there has been a general reluctance to include iron pyrites in commercial blasting compositions. High-density, high-strength blasting compositions now available commercially usually contain ferrosilicon or ferrophosphorus as high density fuels. While these compositions are effective in producing explosives of high density and energy, there is question if the reaction during detonation is complete and permits full utilization of the theoretical available energy.

This invention provides low-cost explosives of high density and strength which can be safely stored and handled at high temperatures. More specifically, this invention comprises an improvement in explosives comprising inorganic oxidizing salt and fuel which improvement comprises of using a fuel component comprising iron sulfide, preferably iron pyrites in combination with antacid. Usually the compositions of this invention contain 0.1 to 5, and preferably 0.25 to 3% antacid, the weight ratio of an iron sulfide to antacid preferably being about from 10-1 to 20-1. Although this mixture can be used by itself to comprise 100% of the fuel component of the explosive mixture, it is preferably used in conjunction with other components which are not per se explosive. Antacid as is used herein to refer to a material which can neutralize mineral acids and when dissolved in a 5% solution of Water yields a pH of greater than 5.

The antacid stabilizer can be one or more of various weakly alkaline substances, e.g., weak bases having a pH of about from 7 to 9 buffering agents, e.g., salts of weak acids and strong bases, hydrogen-ion absorbers, or ionexchange resins which will counteract the acidity in the compositions caused by the addition of the iron sulfides. Suitable antacid substances include buffering agents such as sodium citrate and magnesium citrate, hydrogen-ion absorbers such as hydrated aluminum hydroxide, ion-exchange resins such as silicates (zeolites) or polyaminemethylene resins, and weakly alkaline substances such as aikaline-earth metal, oxides and hydroxides and carbonates and bicarbonates of alkali and alkaline-earth metals such as calcium carbonate, calcium bicarbonate, zinc oxide, magnesium oxide, magnesium hydroxide, magnesium carbonate, sodium carbonate, or sodium bicarbonate. Strong bases generally are avoided with compositions wherein the oxidizing salt is primarily ammonium nitrate, since they tend to react exothermically with the ammonium nitrate, releasing undesirable ammonia in storage. Calcium carbonate, e.g., chalk, is preferred because of its availability, inertness in the system, ease of incorporation into the explosive composition, and relatively low cost. The amount of antacid used can be about from 0.1 to 5.0%, and preferably about from 0.25 to 3% of the total weight of the explosive composition.

The iron sulfide employed in compositions according to this invention can be any of the sulfides of iron, e.g., iron monosulfide, FeS, iron disulfide, FeS iron trisulfide, Fe S and iron tetrasulfide, Fe S or a combination thereof but preferably is provided in the form of iron pyrites, a commercial product comprising essentially FeS and thus containing abouf 47% iron and about 53% sulfur. The iron pyrites usually also contain impurities in the form of small amounts of one or more of free or.

chemically combined copper, arsenic, nickel, cobalt, gold, and selenium and inerts such as sand and quartz. The iron pyrites incorporated in the nitrocarbonitrate blasting agents of this invention preferably are finely-divided and usually have a particle size smaller than about 15 mesh,-

preferably about from 20 to mesh, U.S. Standard sieve. The specific gravity of the iron pyrites is high, usually about 5.0 This high specific gravity is advantageous in that it permits the formulation of compositions of high bulk density. Since the iron sulfides are more reactive chemically than substances such as ferrosilicon and ferrophosphorus which have been used heretofore to increase the bulk density of blasting compositions but may not react completely during detonation, they react more completely during detonation of the composition and provide a composition of higher level of useful energy for blasting than comparable compositions containing ferrophosphorus or ferrosilicon. Usually the iron sulfide will comprise about from 1 to 10% by Weight of the blasting composition.

The. antacid can be combined with the other ingredients of the blasting composition during conventional mixing of these compositions. However, to insure homogeneity the antacid and pyrites are preferably combined in a premixing step prior to their incorporation in the blasting agent. As mentioned above, the presence of the antacid stabilizer is of particular value when the compositions are to contain ingredients such as dinitrotoluene, a high viscosity oil, trinitrotoluene, or resins which require that heat be applied during at least one step of the mixing'to insure complete commingling of the ingredients. Without the presence of the antacid stabilizer, the compositions containing iron sulfides tend to fume-oif and to build up sufiicient heat to cause product fires.

The iron sulfides and stabilizers can be incorporated, as metallic fuel, in any of the known types of blasting compositions which comprise mixtures of at least one inorganic oxidizing salt and a sensitizing fuel. The compositions usually contain at least about 20% by weight of the inorganic salt. Such salts can include, for example, at least one of the ammonium, alkali, and alkaline-earth metal nitrates and perchlorates, such as ammonium nitrate, ammonium perchlorate, sodium nitrate, sodium perchlorate, potassium nitrate, potassium perchlorate, magnesium nitrate, magnesium perchlorate, and calcium nitrate. Preferably, at least about 45% by weight of the inorganic oxidizing salts employed is ammonium nitrate, either alone or in combination with sodium nitrate.

Although the iron sulfide can comprise the whole of the sensitizing fuel, it is preferably used in combination with at least one other fuel. The auxiliary fuels employed in the compositions of this invention can be varied widely, provided that in the compositions in which the fuel is employed with iron sulfides it is stable, i.e., chemically inert, during preparation and handling prior to intentional actuation of the composition by an initiator or primer of a predetermined explosive strength. This fuel can be, for example, a self-explosive composition, a carbonaceous fuel, or a metal in addition to the iron sulfide and antacid stabilizer.

Self-explosive fuels include TNT, pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), nitrostarch, smokeless powder, explosive-grade nitrocellulose, tetryl, and the like, as well as mixtures of at least two of the aforementioned self-explosive fuels, such as, for example, pentolite (PETN/TNT), Composition B (RDX/TNT), and tetratol (tetryl/TNT).

Examples of carbonaceous, non-explosive fuels which can be used in this invention include finely-divided carbons such as coal, graphite, soot, lampblack, and coke; solid carbonaceous vegetable products such as flours and starches or corn, wheat and other cereal products, wood pulps and meals, ground nut hulls or fruit pits, sugars, bagasse, plant fibers, and gums; organic liquids such as hydrocarbon (petroleum-derived) oils, fatty oils, and vegetable oils, urea; monoand dinitro-aromatics such as monoand dinitrotoluene and mixtures of at least two of the aforementioned carbonaceous fuels.

Auxiliary metallic fuels which can be used in this invention include any metal or alloy capable of rapid oxidation. These can include, for example, aluminum, magnesium, manganese, nickel, and iron and alloys of such metals with each other and with other elements such as silicon, sulfur, and phosphorus, e.g., aluminum-magnesium alloys, ferrosilicon and ferrophosphorus; as well as mixtures of these. The amounts of fuel vary widely with the particular fuel employed and the explosive characteristics desired of a particular composition. In general, less than about 35% and preferably about from 5 to 30% by weight, based on the weight of the explosive composition, of a self-explosive fuel is used. Less than about 25% and preferably about from 2 to by weight (of the explosive composition) of carbonaceous fuels are commonly employed, and usually up to about by weight (based on weight of the explosive composition) of light metals such as aluminum are used. The total weight of the iron sulfide antacid stabilizer and heavy metal-containing substances, e.g., ferrophosphorus and ferrosilicon, comprise about from 1 to 20% by weight of the composition. Compositions in accordance with this invention will usually have an oxygen balance of about from 0 to 20%, and preferably 2 to 17%.

In the following examples, which further illustrate the instant invention, parts are by weight unless otherwise 4 indicated. The iron sulfides in these examples is commercial iron pyrites having a specific gravtiy of 5.0, and the particle size is such that passes a 20 mesh US. Standard sieve and 35% passes a 100 mesh sieve. The pH of the dry composition is determined by (1) mixing all dry ingredients,

(2) adding liquid fuels and mixing,

(3) mixing 50 g. of H 0 with each 100 g. of the composition, and

(4) ascertaining the pH of the composition by conventional wet methods, e.g., a Beckman pH meter.

Example 1 To a mixer containing 86 parts of ammonium nitrate prills (less than 5% of which passes a 20 mesh screen (US. Standard series)) is added a premixed blend of iron pyrites (9.5 parts by weight of the composition) and finely-divided calcium carbonate comprising 0.5 part by weight of the composition having a particle size such that 100% passes through a 35 mesh screen. This mixture is blended for about five minutes, and 4 parts of high-flashpoint, high viscosity oil (Ebony P oil available from Atlantic Refining Co.) and 1 part of anti-setting agent (Attacote) are added. Mixing is continued for an additional 15 minutes to assure homogeneity. The pH of this composition is 6.9.

A second composition is prepared for comparative purposes in the same manner except that the calcium carbonate is omitted and the composition contains 10% iron pyrites. The pH of this composition is 6.6.

Fifty-gram samples of each composition are charged into glass tubes (25 mm. x 200 mm.), each containing a thermocouple suspended in the composition near the midpoint. The containers are suspended for 24 hours in an oil bath heated to 300 F. (159 0). During the testing, the second composition, which contains no calcium carbonate, evolves fumes, and shows evidence of internal heat, the temperature of the composition is indicated by the thermocouples exceeding that of the bath by about 200 F. However the composition containing calcium carbonate showed no evidence of internal heating or fume-offs over the twenty-four hour period. Similar results are obtained when magnesium oxide (MgO) and when sodium bicarbonate (NaHCO are incorporated in the composition as antacids (in lieu of chalk) in proportions of 1 part of MgO or NaHCO per 20 parts of iron pyrites (about /2 pound of antacid per 100 pounds of composition).

Example 2 Blasting compositions of the formulations shown below are prepared as described in Example 1 and are loaded into cartridges 3 /2 inches in diameter.

l Grams of PETN needed to initiate detonation in 3% inch diameter cartridges.

Field tests of the compositions A and B described above' in a trona mine reveal that the compositions show excellent rock breakage and burden movement, and showed little or no toxic gases.

Example 3 Eighty-three parts of ammonium nitrate prills, a blend of 9.5 parts iron pyrites and 0.5 part calcium carbonate, two parts coal one part antisetting agent and one part of high-viscosity oil are blended together and heated to Example 4 Blasting agents of the formulations shown in Table II, below, are prepared by blending ammonium nitrate prills, iron pyrites or iron pyrites-chalk blend, and oil, heating the mixture to 100 F., and adding dinitrotoluene. Mixing is continued, with heating, until a homogeneous blend is obtained. The products are loaded into cylindrical metal containers (8 inch x 8 inch), each holding 10 pound samples, and suspended in an oil bath maintained at 250 F. Thermocouples are inserted into the composition in each container. Results of the tests are as shown in Table II. Fume-off indicates that the sample builds up sufiicient internal heat to cause rapid exothermic decomposition and complete burning, stable indicates that there is no evidence of internal heat build-up.

TAB LE II Composition 1 Stable. 2 Fume-off.

Example 5 Ammonium nitrate 95% retained on mesh screen 5.0 Ammonium nitrate retained on 100 49.0

mesh screen) 44.00 Sodium nitrate 30.0 Fuel oil (Ebony P) 1.0 Calcium stearate 0.5 Dinitrotoluene 9.0 Iron pyn'tes 9.5 Calcium carbonate 0.5

pH of composition 6.4 Oxygen balance -2.5 Packed density 1.48 Detonation velocity, m./sec 4250 Sensitivity, expressed as gr. of PETN needed to initiate detonation g 2.64

Based on 'No. 8 cap containing 6.8 grains PETN.

Example 6 Compositions of the formula shown below are prepared by the procedure shown in Example 5. These compositions are formulated to about the same oxygen balance.

Ammonium nitrate 83.0 Fuel oil (Ebony P) 1.0 Iron pyrites 9.5 Calcium carbonate 0.5 Antisetting agent 1.0 Dinitrotoluene 3.0 Coal 2.0 Packed density 1.15 Oxygen balance 2.2 Detonation velocity, m./sec. 4250 Cap sensitivity grams PETN 1.76

4 No. 8 caps.

Field tests of the above described composition as a top load in S-inch diameter holes in rock quarry reveal that in terms of rock breakage and burden movement the composition is excellent.

I claim:

1. In an explosive composition comprising inorganic oxidizing salt and fuel, the improvement which comprises using, in combination, (a) a fuel component comprising at least one iron sulfide and (b) at least one antacid.

2. An explosive composition of claim 1 wherein said antacid is selected from the group consisting of alkalineearth metal oxides and hydroxides and alkali and alkalineearth metal carbonates and bicarbonates.

3. An explosive composition of claim 2 wherein said iron sulfide is iron pyrites.

4. An explosive composition of claim 3 wherein said inorganic oxidizing salt component comprises at least one of ammonium nitrate and sodium nitrate.

5. An explosive composition of claim 4 wherein said antacid comprises about from 0.1 to 5.0% by Weight of the explosive composition.

6. An explosive composition of claim 5 having, as auxiliary fuel in addition to the iron sulfide, a hydrocarbon.

7. An explosive composition of claim 5 having, as auxiliary fuel in addition to the iron sulfide, dinitrotoluene.

References Cited UNITED STATES PATENTS 1,318,709 10/1919 Vautin 149-37 CARL D. QUARFORTH, Primary Examiner. L. DEWAYNE RUTLEDGE, Examiner.

S. I. LECHERT, JR., Assistant Examiner.